GROSS ANATOMY OF DORSUM OF HAND.pdf

# Gross anatomy of the dorsum of the hand This section details the superficial and deep anatomical structures located on the back of the hand. ### 1.1 Superficial structures #### 1.1.1 Skin The skin covering the dorsum of the hand is thin and can be easily lifted from the underlying deep fascia and tendons due to a scarcity of subcutaneous fat. It is also freely mobile over these deeper structures [2](#page=2). #### 1.1.2 Superficial fascia The superficial fascia on the dorsum of the hand contains cutaneous nerves, the dorsal venous plexus, and the dorsal carpal arch [3](#page=3) [7](#page=7). ##### 1.1.2.1 Cutaneous innervation The sensory innervation of the dorsum of the hand is primarily supplied by the terminal or superficial branches of the radial nerve and the dorsal branch of the ulnar nerve [3](#page=3). * The terminal branch of the radial nerve innervates the lateral three and a half digits of the dorsum, providing digital branches to the thumb, index finger, middle finger, and the lateral half of the ring finger. These nerve endings do not extend as far as the nail beds [3](#page=3). * The dorsal branch of the ulnar nerve innervates the medial one and a half digits of the dorsum, providing digital branches to the little finger and the medial half of the ring finger [3](#page=3). ##### 1.1.2.2 Dorsal venous network A prominent dorsal venous network is present on the dorsum of the hand, which receives drainage from the palm, ensuring that venous return is not impeded during gripping activities. This network is situated proximal to the metacarpal heads [5](#page=5). * On the radial side, the network drains into the cephalic vein [5](#page=5). * On the ulnar side, it drains into the basilic vein [5](#page=5). The digital veins from the adjacent sides of the index, middle, ring, and little fingers merge to form three dorsal metacarpal veins on the dorsum of the hand. The lateral end of this venous arch connects with digital veins from the index finger and thumb to contribute to the cephalic vein. The medial end of the arch receives a single digital vein from the medial side of the little finger before joining to form the basilic vein [5](#page=5). #### 1.1.3 Dorsal carpal arch The dorsal carpal arch is an arterial anastomosis located on the back of the carpus, formed by the radial, ulnar, and anterior interosseous arteries. It gives off dorsal metacarpal arteries that descend into the intermetacarpal spaces. These arteries lie deep to the long extensor tendons and supply the adjacent sides of the index, middle, ring, and little fingers. These dorsal metacarpal arteries also communicate with the palmar metacarpal branches of the deep palmar arch and the palmar digital branches of the superficial arch through the interosseous spaces [7](#page=7). ### 1.2 Deep structures #### 1.2.1 Deep fascia The deep fascia on the dorsum of the hand is modified to form the extensor retinaculum [9](#page=9). #### 1.2.2 Spaces on the dorsum of the hand There are two distinct spaces on the dorsum of the hand: * **Dorsal subcutaneous space:** This space is located directly beneath the skin and is characterized by its looseness, allowing the skin to be easily lifted [9](#page=9). * **Dorsal subtendinous space:** This space lies deep to the extensor tendons, situated between the tendons and the metacarpal bones [9](#page=9). * * * # The anatomical snuff box The anatomical snuff box is a clinically significant triangular depression on the radial side of the wrist that serves as a landmark for important anatomical structures and has implications in injury assessment. ### 2.1 Definition and observation The anatomical snuff box is a triangular depression located on the radial (lateral) side of the dorsum of the wrist. Its name derives from its historical use for holding and inhaling powdered tobacco (snuff). This depression is most apparent when the thumb is extended [13](#page=13). ### 2.2 Boundaries The anatomical snuff box is defined by specific anatomical borders: * **Anterior (radial/lateral) border:** Formed by the tendons of the \_extensor pollicis brevis and \_abductor pollicis longus muscles [13](#page=13). * **Posterior (ulnar/medial) border:** Formed by the tendon of the \_extensor pollicis longus muscle [13](#page=13). * **Floor:** Composed of palpable bony structures, from proximal to distal, including the radial styloid process, the scaphoid bone, the trapezium bone, and the base of the first metacarpal [14](#page=14). * **Roof:** Consists of the skin and fascia overlying the depression [14](#page=14). ### 2.3 Contents Several important structures are found within the anatomical snuff box: * **Radial artery:** This artery lies deep to all three tendons forming the borders and can be palpated in the floor of the snuff box [14](#page=14). * **Superficial cutaneous branch of the radial nerve:** This nerve innervates the dorsal surface of the lateral three and a half digits and the corresponding area on the dorsum of the hand [14](#page=14). * **Cephalic vein:** The origin of the cephalic vein is in the roof of the snuff box, arising from the radial side of the dorsal venous network [14](#page=14). ### 2.4 Clinical relevance The anatomical snuff box holds significant clinical importance: * **Palpation of the radial pulse:** The radial pulse can be readily palpated in the proximal part of the anatomical snuff box, making it a common site for clinical pulse assessment [16](#page=16). * **Scaphoid fracture:** Tenderness and pain localized to the anatomical snuff box are characteristic signs of a scaphoid fracture. The scaphoid is the most frequently fractured carpal bone, often resulting from a fall onto an outstretched hand [16](#page=16). * **Avascular necrosis risk:** The scaphoid is particularly susceptible to avascular necrosis following a fracture due to its retrograde blood supply, which enters at the distal end of the bone [16](#page=16). > **Tip:** When assessing for a potential scaphoid fracture, palpating for tenderness directly within the anatomical snuff box is a crucial diagnostic step. > **Example:** A patient presents with wrist pain after a fall. On physical examination, the clinician notes significant tenderness upon palpation of the anatomical snuff box. This finding strongly suggests a possible scaphoid fracture, prompting further investigation such as X-rays. * * * # Flexor retinaculum and carpal tunnel The flexor retinaculum forms the roof of the carpal tunnel, a critical passageway for nerves and tendons in the wrist. ### 3.1 The flexor retinaculum The flexor retinaculum is a robust fibrous band situated on the palmar aspect of the hand, measuring approximately 2-3 cm transversely and longitudinally. It spans the front of the carpus at the proximal part of the hand [17](#page=17). #### 3.1.1 Attachments of the flexor retinaculum * **Proximal attachment:** Lies at the level of the distal dominant skin crease on the front of the wrist [17](#page=17). * **Medial attachment:** Attaches to the hook of the hamate and the pisiform [17](#page=17). * **Lateral attachment:** Attaches to the tubercle of the scaphoid and the ridge of the trapezium [17](#page=17). #### 3.1.2 Relationships and continuity The flexor retinaculum functions as the roof of the carpal tunnel, with the carpal bones forming the floor. It is continuous proximally with the palmar carpal ligament and, more deeply, with the palmar aponeurosis [18](#page=18). ### 3.2 The carpal tunnel The carpal tunnel is a narrow fibro-osseous canal located on the anterior aspect of the wrist. It is formed by a bony gutter created by the carpal bones and is covered by the flexor retinaculum, which acts as its roof. The carpal arch, comprising the carpal bones, forms the base and sides of the tunnel [18](#page=18) [20](#page=20). #### 3.2.1 Contents of the carpal tunnel The carpal tunnel houses the median nerve and all the long flexor tendons for the fingers and thumb, totaling nine tendons. These tendons are enveloped by synovial sheaths, which facilitate their smooth movement [20](#page=20) [21](#page=21). The contents include: * Median nerve [20](#page=20) [21](#page=21). * Tendon of flexor pollicis longus [21](#page=21). * Four tendons of flexor digitorum profundus [21](#page=21). * Four tendons of flexor digitorum superficialis [21](#page=21). The eight tendons of the flexor digitorum profundus and superficialis share a single synovial sheath. In contrast, the tendon of the flexor pollicis longus has its own distinct synovial sheath. The tendon of the flexor carpi radialis also passes through a sub-compartment of the carpal tunnel within its own synovial sheath, residing in a groove on the radial side [21](#page=21). > **Tip:** It is important to note that the palmar cutaneous branch of the median nerve arises \_before the median nerve enters the carpal tunnel, which is why this branch is typically spared in conditions affecting the carpal tunnel [20](#page=20). #### 3.2.2 Structures passing superficial to the carpal tunnel Several structures traverse superficial to the carpal tunnel, distinct from its contents [22](#page=22): * Ulnar nerve and artery [22](#page=22). * Tendon of Palmaris longus [22](#page=22). * Palmar cutaneous branch of the median nerve [22](#page=22). * Palmar cutaneous branch of the ulnar nerve [22](#page=22). * Superficial palmar branch of the radial artery [22](#page=22). ### 3.3 Clinical relevance: Carpal tunnel syndrome Carpal tunnel syndrome is a common clinical condition arising from the compression of the median nerve within the carpal tunnel. It is recognized as the most prevalent mononeuropathy [23](#page=23). #### 3.3.1 Causes of carpal tunnel syndrome Potential causes include: * Arthritic changes in the wrist joint [23](#page=23). * Thickening of the synovial sheath [23](#page=23). * Edema (swelling) [23](#page=23). #### 3.3.2 Symptoms of carpal tunnel syndrome Symptoms typically manifest due to median nerve compression and include: * Wasting and weakness of the thenar muscles [23](#page=23). * Loss of the power of thumb opposition [23](#page=23). * A burning or tingling sensation affecting three and a half digits on the radial side of the hand [23](#page=23). * * * # Palmar aponeurosis and fascial spaces of the hand The palmar aponeurosis is a strong, triangular fascial sheet in the palm that, along with its extensions, forms compartments housing crucial structures and plays a role in hand mechanics and pathology. ### 4.1 Palmar aponeurosis The palmar aponeurosis, also known as the palmar fascia, is a dense connective tissue that invests the intrinsic muscles of the palm. It is organized into central, lateral, and medial parts [24](#page=24). #### 4.1.1 Central part of the palmar aponeurosis The central part is the most prominent, occupying the middle of the palm and possessing significant strength [24](#page=24). * **Proximal continuity:** It is continuous proximally with the flexor retinaculum [24](#page=24). * **Tendon attachment:** It receives the expanded tendon of the palmaris longus muscle [24](#page=24). * **Distal division:** Distally, it widens and divides into four fibrous strips, each extending to one of the fingers [24](#page=24). * **Digital slips:** Each digital slip sends superficial fibers to the skin of the distal palm and attaches to the skin at the base of each digit [25](#page=25). * **Deeper attachments:** The deeper portion of each digital slip bifurcates into two divergent bands. These bands insert into the deep transverse metacarpal ligament, the bases of the proximal phalanges, and the fibrous flexor sheaths of the digits [25](#page=25). * **Superficial fascia and muscle origin:** The central part is closely adherent to the skin via dense fibroareolar tissue, forming the superficial palmar fascia. The palmaris brevis muscle originates from its medial margin [25](#page=25). #### 4.1.2 Lateral and medial parts of the palmar aponeurosis The lateral and medial parts are thinner fibrous layers [26](#page=26). * **Lateral part:** Covers the thenar muscles on the radial side of the hand [26](#page=26). * **Medial part:** Covers the muscles of the little finger (hypothenar muscles) on the ulnar side [26](#page=26). * **Continuity:** Both parts are continuous with the central portion of the aponeurosis and with the fascia on the dorsum of the hand [26](#page=26). #### 4.1.3 Superficial transverse metacarpal ligament A thickening of transversely oriented fibers at the level of the metacarpal heads forms the superficial transverse metacarpal ligament, also known as the natatory ligament [26](#page=26). #### 4.1.4 Clinical relevance of the palmar aponeurosis * **Dupuytren's contracture:** This condition results from the thickening and subsequent contracture of the palmar aponeurosis and its digital slips [28](#page=28). * **Risk factors:** Include excessive smoking and genetic predisposition [28](#page=28). * **Pathology:** Characterized by fibroblast proliferation and deposition of type III collagen [28](#page=28). * **Manifestation:** Leads to fixed flexion of the affected fingers, commonly the ring and little fingers [28](#page=28). ### 4.2 Fascial spaces of the hand The fascial spaces of the hand are divided into palmar and dorsal compartments, which are crucial for understanding the spread of infection and the anatomy of the hand [30](#page=30). #### 4.2.1 Palmar spaces These are compartments within the palm, located between the wrist joint and the phalanges. They are formed by fibrous septa extending from the palmar aponeurosis [30](#page=30) [31](#page=31). ##### 4.2.1.1 Hypothenar space * **Location:** Situated medially, lateral to the fibrous septum extending from the ulnar side of the palmar aponeurosis to the palmar border of the fifth metacarpal bone [31](#page=31). * **Contents:** Houses the hypothenar muscles: abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi [31](#page=31). ##### 4.2.1.2 Midpalmar space * **Location:** Occupies the central part of the palm, deep to the flexor tendons of the fingers. It is separated from the thenar space by a septum originating from the radial side of the palmar aponeurosis, which inserts onto the palmar surface of the middle metacarpal [31](#page=31). * **Proximal boundary:** Enclosed proximally by the thin attachment of the parietal layer of the common flexor synovial sheath to the walls of the carpal tunnel [31](#page=31). ##### 4.2.1.3 Thenar space * **Location:** Situated on the radial side of the palm, overlaid by the flexor tendons to the index finger [32](#page=32). * **Contents:** Contains the first lumbrical muscle [32](#page=32). ##### 4.2.1.4 Pulp space * **Location:** Found at the tips of the fingers and thumb [32](#page=32). * **Structure:** Composed of fatty tissue compartmentalized by fibrous septa that extend from the distal phalanx to the skin [32](#page=32). * **Vascular supply:** Terminal branches of digital vessels traverse these spaces to supply the distal phalanx [32](#page=32). * **Proximal limit:** The skin's firm adherence to the underlying tissue at the distal flexion crease prevents pulp infections from spreading proximally along the finger [32](#page=32). #### 4.2.2 Dorsal spaces These are located on the dorsum of the hand. ##### 4.2.2.1 Dorsal subcutaneous space * **Location:** Situated immediately deep to the loose skin on the dorsum of the hand [33](#page=33). ##### 4.2.2.2 Dorsal subaponeurotic space * **Location:** Lies between the metacarpal bones and the extensor tendons, which are interconnected by a thin aponeurosis [33](#page=33). #### 4.2.3 Clinical relevance of fascial spaces * **Spread of infection:** Infections within the midpalmar space can extend into the carpal tunnel, potentially involving the three ulnar lumbricals [34](#page=34). * **Pulp space infections:** Infections in the pulp spaces can lead to occlusion of the digital vessels, potentially causing necrosis of the distal bone [34](#page=34). > **Tip:** Understanding the fascial planes and their boundaries is crucial for surgical interventions and for predicting the spread of infections in the hand. The continuity of these spaces with deeper structures, like the carpal tunnel, highlights the importance of prompt and accurate diagnosis of hand infections. * * * ## Common mistakes to avoid * Review all topics thoroughly before exams * Pay attention to formulas and key definitions * Practice with examples provided in each section * Don't memorize without understanding the underlying concepts

| Term | Definition | |---|---| | Dorsum of the hand | The posterior surface of the hand, commonly referred to as the back of the hand. | | Superficial fascia | The layer of loose connective tissue located beneath the skin, containing nerves, blood vessels, and fat. | | Cutaneous nerves | Nerves that provide sensory innervation to the skin. | | Dorsal venous plexus | A network of veins on the back of the hand that collects deoxygenated blood. | | Dorsal carpal arch | An arterial anastomosis on the back of the wrist formed by branches of the radial, ulnar, and anterior interosseous arteries. | | Extensor retinaculum | A broad, thickened band of deep fascia at the wrist that holds the extensor tendons in place, preventing them from bowstringing. | | Anatomical snuff box | A triangular depression on the radial side of the dorsum of the wrist, formed by the tendons of specific thumb muscles. | | Scaphoid fracture | A fracture of the scaphoid bone, one of the carpal bones in the wrist, often associated with pain and tenderness in the anatomical snuff box. | | Flexor retinaculum | A strong fibrous band located on the palmar side of the wrist that forms the roof of the carpal tunnel. | | Carpal tunnel | A narrow passageway in the wrist formed by the carpal bones and the flexor retinaculum, containing the median nerve and flexor tendons. | | Carpal tunnel syndrome | A condition caused by compression of the median nerve within the carpal tunnel, leading to symptoms like pain, numbness, and weakness in the hand. | | Palmar aponeurosis | A strong, triangular-shaped fascial sheet in the palm of the hand that provides a protective covering and attachment for muscles. | | Fascial spaces of the hand | Compartmentalized areas within the hand, separated by fascial septa, that can be involved in the spread of infection. | | Thenar space | A fascial space in the palm of the hand, located on the radial side, medial to the thenar eminence. | | Midpalmar space | A large fascial space in the central part of the palm, deep to the palmar aponeurosis. | | Hypothenar space | A fascial space on the ulnar side of the palm, associated with the muscles of the little finger. | | Pulp space | The space within the fatty pad at the tips of the fingers and thumb, which is divided by fibrous septa. |